The present invention relates to an IC temperature sensor used for electrical products.
An IC temperature sensor which can be formed by the same process as CMOS and which NPN bipolar transistors are connected in a Darlington circuit is described in Japanese Patent No. S59-47467. FIG. 5 is a circuit diagram of NPN bipolar transistors connected in a double Darlington circuit and a constant current circuit is connected to an emitter of a transistor 102. This circuit detects the sum Vout of a voltage between a base and an emitter of a transistor 101 and a voltage between a base and the emitter of the transistor 102. An example of double collector construction applied to transistor 102 of FIG. 5 is shown in FIG. 13. In the above IC temperature sensor, current I1 between base and emitter of first transistor 101 is 1/.beta. of current I2 between base and emitter of second transistor 102. As it is so small, the IC temperature sensor has had a problem to be sensitive to noise. Here, .beta. is current-amplification factor of transistor 102. Further, the IC temperature sensor has had a problem that current-amplification factor .beta. deviated, I1 deviated, and detecting voltage Vout deviated much.
Although a construction of transistor for making .beta. small is shown, the above problem has not been solved because .beta. does not become small, only about 10. When more than triple transistors are connected, deviation of detecting voltage Vout is large. The triple transistors is the limit practically.
The IC temperature sensor has had another problem that current consumption of the IC became large because large current must flow through the last transistor to make stable by flowing some current through the first transistor. Because of the problem, the area of the last transistor becomes large and the cost of the IC becomes high.
The IC temperature sensor has had a problem that current flowing through transistors except last transistor changed according to temperature and the more the connection of transistor were, the worse the linearity of detecting voltage Vout became.
The IC temperature sensor has had a problem that processes increase because different impurity concentration regions such as base region and emitter region of bipolar transistors, and well region and each source drain region of N and P types of CMOS had to be formed.
The IC temperature sensor has had a problem that temperature linearity of detecting voltage became bad because there was a difference between mobility temperature characteristics of well region of CMOS transistor assuming temperature characteristics of a constant current circuit and mobility temperature characteristics of base region assuming temperature characteristics of a bipolar transistor. The IC temperature sensor has had a problem that detecting voltage peredetermined current became small by making impurity concentration of base region high and constant current for gaining the specified detecting voltage became large.
The IC temperature sensor has had a problem that effective area of junction between base and collector was influenced by diffusion distance of minority carrier in base, and .beta. was easy to deviate.
Therefore, in order to solve the problems, the object of the present invention is to provide an IC temperature sensor which is low cost, small current consumption, small deviation of detecting voltage, and superior anti-noise characteristics and linearity of detecting voltage.